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Overview

Distribution

Indo-Pacific bottlenosed dolphins tend to live in shallow water near the shore at depths of less than 300 m. The habitat of some Indo-Pacific bottlenosed dolphins is estuarine but spatial distribution of dolphins varies depending on season and tidal state. These variables influence water temperature and prey distribution.

Biogeographic Regions: indian ocean (Native ); pacific ocean (Native )

  • Fury, C., P. Harrison. 2008. Abundance, site fidelity, and range patterns of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in two Australian subtropical estuaries. Marine and Freshwater Research, 59/11: 1015-1027.
  • Fury, C., P. Harrison. 2011. Seasonal variation and tidal influences on estuarine use by bottlenose dolphins (Tursiops aduncus). Estuarine, Coastal and Shelf Science, 93/4: 389-395.
  • Kogi, K., T. Hishii, A. Imamura, T. Iwatani, K. Dudzinski. 2004. Demographic parameters of indo-pacific bottlenose dolphins (Tursiops aduncus) around Mikura Island, Japan. Marine Mammal Science, 20/3: 510-526.
  • Kurihara, N., S. Oda. 2007. Cranial variation in bottlenose dolphins Tursiops spp. from the Indian and western Pacific Oceans: additional evidence for two Species. Acta Theriologica, 52/4: 403-418.
  • Nowak, R. 2003. Walker's Marine Mammals of the World. Baltimore, MD: John Hopkins University Press.
  • Saayman, G., C. Tayler, D. Bower. 1973. Diurnal Activity Cycles in Captive and Free-Ranging Indian Ocean Bottlenose Dolphins (Tursiops aduncus Ehrenburg). Behavior, 44/3-4: 212-232.
  • Shirihai, H., B. Jarrett. 2006. Whales, Dolphins, and Other Marine Mammals of the World. Princeton, NJ: Princeton University Press.
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Range Description

The Indo-Pacific Bottlenose Dolphin has a discontinuous distribution in the warm temperate to tropical Indo-Pacific, from South Africa in the west, along the rim of the Indian Ocean (including the Red Sea, Persian Gulf and Indo-Malay Archipelago as far east as the Solomon Islands and possibly New Caledonia) to the southern half of Japan and southeast Australia in the east (Wells and Scott 2002, Möller and Beheregaray 2001). It is also found around oceanic islands distant from major land masses within this range.

The map shows where the species may occur based on oceanography. The species has not been recorded for all the states within the hypothetical range as shown on the map. States for which confirmed records of the species exist are included in the list of native range states. States within the hypothetical range but for which no confirmed records exist are included in the Presence Uncertain list.
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Distribution in Egypt

Red Sea.

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Physical Description

Morphology

Tursiops aduncus are similar to Tursiops truncatus in form with a fusiform body, dorsal fin, and beak. The dorsal surface is slate blue or dark gray, with darker flippers and extremities and lighter, often pink-tinted, undersides. Patterning and ventral spotting vary by age and geographic location. A recent study has claimed that ventral spotting may be a sign of reproductive maturity, especially in females.

Adult Indo-Pacific bottlenosed dolphins have a head and body length between 175 and 400 cm, a pectoral fin length of about 23 cm, and a tail fluke expanse of 60 cm. Their weight is about 230 kg. Adult female Tursiops aduncus have been measured to be 200 cm in length in certain regions, while adult males are usually longer and heavier than females. Females have a single external opening and males have distinct anal and genital openings.

Like most bottlenosed dolphins, Indo-Pacific bottlenose dolphins have conical, single-rooted, unicuspid, homodont teeth that are about 1 cm in diameter. However, tooth counts alone usually cannot be used to differentiate T. aduncus and T. truncatus. In general, bottlenosed dolphins have between 20 and 28 teeth on each side of the jaw. Another cranial feature is the concavity of the top of the rostrum between the anterior edge of the nares and the distal tip of the premaxillae.

There are a number of physical differences between T. truncatus and T. aduncus. Indo-Pacific bottlenosed dolphins can be distinguished from T. truncatus by ventral spotting in adult specimens which increases with age, a longer, better-defined rostrum, a smaller melon, and, in some cases, more teeth. Indo-Pacific bottlenosed dolphins also have a smaller body, a smaller head, and larger flippers than T. truncatus. They have a more slender rostrum that is tapered more abruptly near the base and taller and broader-based dorsal fins relative to other bottlenosed dolphins. However, these differences are variable, which can make it difficult to distinguish them in areas of overlap.

With rapid gas exchange at the capillaries, double the amount of erythrocytes, and about 2 to 9 times the amount of myoglobin of land animals, dolphins are able to alternate between no breathing while deep diving and normal breathing while swimming along the surface.

Average mass: 230 kg.

Range length: 175 to 400 cm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: male larger

  • Krzyszczyk, E., J. Mann. 2012. Why become speckled? Ontogeny and function of speckling in Shark Bay bottlenose dolphins (Tursiops spp.). Marine Mammal Science, 28/2: 295-307.
  • Mann, J., R. Connor, L. Barre, M. Heithaus. 2000. Female reproductive success in bottlenose dolphins (Tursiops sp.): life history, habitat, provisioning, and group-size effects. Behavioral Ecology, 11/2: 210-219.
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Ecology

Habitat

Indo-Pacific bottlenosed dolphins tend to live in shallow water near the shore at depths of less than 300 m. With rapid gas exchange at the capillaries, double the amount of erythrocytes, and about 2 to 9 times the amount of myoglobin of land animals, dolphins are able to alternate between no breathing while deep diving and normal breathing while swimming along the surface.

Range depth: 2 to 300 m.

Habitat Regions: tropical ; saltwater or marine

Aquatic Biomes: reef ; coastal ; brackish water

Other Habitat Features: estuarine

  • Martin, R., R. Pine, A. DeBlase. 2001. A Manual of Mammalogy with Keys to Families of the World. Long Grove, IL: Waveland Press, Inc.
  • Vaughan, T., J. Ryan, N. Czaplewski. 2011. Mammalogy. Boston, MA: Jones & Bartlett Learning.
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Habitat and Ecology

Habitat and Ecology
Indo-Pacific Bottlenose Dolphins generally occur over shallow coastal waters on the continental shelf or around oceanic islands. They sometimes occur in mixed groups with Common Bottlenose Dolphins and other delphinid species. They feed on a wide variety of schooling, demersal and reef fishes, as well as cephalopods (Ross 1984; J.Y. Wang, unpubl. data).

Systems
  • Marine
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tropical to temperate, coastal
  • UNESCO-IOC Register of Marine Organisms
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Depth range based on 120 specimens in 1 taxon.
Water temperature and chemistry ranges based on 72 samples.

Environmental ranges
  Depth range (m): 0 - 0
  Temperature range (°C): 27.353 - 28.694
  Nitrate (umol/L): 0.038 - 0.346
  Salinity (PPS): 33.213 - 34.984
  Oxygen (ml/l): 4.437 - 4.664
  Phosphate (umol/l): 0.097 - 0.169
  Silicate (umol/l): 3.208 - 6.205

Graphical representation

Temperature range (°C): 27.353 - 28.694

Nitrate (umol/L): 0.038 - 0.346

Salinity (PPS): 33.213 - 34.984

Oxygen (ml/l): 4.437 - 4.664

Phosphate (umol/l): 0.097 - 0.169

Silicate (umol/l): 3.208 - 6.205
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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Trophic Strategy

Indo-Pacific bottlenosed dolphins have a diet consisting of mainly bony fish and, to a lesser degree, cephalopods. While they eat a wide variety of fish species, the majority of their diet is composed of just a few species, which varies regionally. In captivity these dolphins eat 6 to 7 kg of food per day. They hunt cooperatively and foraging behavior is characterized by shallow dives multiple times per minute. In shallow water they hunt by using several methods, including “kicking” fish into the sand with their tails and chasing small fish up on to the shore. While feeding and traveling they leap from the water regularly. Hunting and feeding occur most frequently in the morning and afternoon.

Animal Foods: fish; mollusks

Primary Diet: carnivore (Piscivore )

  • Amir, O., P. Berggren, S. Ndaro, N. Jiddawi. 2005. Feeding ecology of the Indo-Pacific bottlenose dolphin (Tursiops aduncus) incidentally caught in the gillnet fisheries off Zanzibar, Tanzania. Estuarine, Coastal and Shelf Science, 63/3: 429-437.
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Associations

Indo-Pacific bottlenosed dolphins are predators of many species of bony fish and squid in coastal tropical waters. Indo-Pacific bottlenosed dolphins are prey of many species of sharks. They often act as hosts for parasites and barnacles. Semi-parasitic barnacles can attach to their skin, causing irritations and drag as they swim.

Ecosystem Impact: keystone species

Commensal/Parasitic Species:

  • Perrin, W., B. Würsig, J. Thewissen. 2008. Encyclopedia of Marine Mammals. San Diego, CA: Academic Press.
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Indo-Pacific bottlenosed dolphins are hunted by at least 10 species of sharks. These predators may have played an important role in the evolution of social behavior in bottlenosed dolphins. By traveling in groups, they are less vulnerable to predators. Humans are also predators because bottlenosed dolphins are hunted and captured for food and entertainment. Their countershaded color pattern also helps to make them harder to see in marine environments.

Known Predators:

Anti-predator Adaptations: cryptic

  • Heithaus, M. 2001. Shark Attacks on Bottlenose Dolphins (Tursiops aduncus) in Shark Bay, Western Australia: Attack Rate, Bite Scar Frequencies, and Attack Seasonality. Marine Mammal Science, 17/3: 526-539.
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Life History and Behavior

Behavior

It has been argued that the large and convoluted brain of Indo-Pacific bottlenosed dolphins allows for greater intelligence and higher-order learning. They communicate via auditory perception. While their sense of sight is not well-developed, their sense of hearing is keen and important in echolocation. Indo-Pacific bottlenosed dolphins generate ultrasonic clicks and interpret the returning signals to perceive objects in their environment. Each dolphin also uses a characteristic whistle that helps other identify them individually. Indo-Pacific bottlenosed dolphins also communicate via tactile signals. Most often, flippers are rubbed over the flippers or bodies of other dolphins of the same sex and age. Flipper rubbing is observed between opposite sexes around mating and between mothers and calves.

Communication Channels: visual ; tactile ; acoustic

Perception Channels: visual ; tactile ; acoustic ; ultrasound ; echolocation ; vibrations ; chemical

  • Sakai, M., T. Hishii, S. Takeda, S. Kohshima. 2006. Flipper rubbing behaviors in wild bottlenose dolphins (Tursiops aduncus). Marine Mammal Science, 22/4: 966-978.
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Life Expectancy

The average lifespan of the Indo-Pacific Bottlenose dolphin in the wild is more than 40 years, while the average age of adult males and females in the wild is 19 years and 26 years, respectively. The oldest known dolphins in the wild are a 39 year old male and a 49 year old female.

Range lifespan

Status: wild:
39 for male, 49 for female (high) years.

Average lifespan

Status: wild:
40+ years.

  • Klinowska, M., J. Cook. 1991. Dolphins, Porpoises and Whales of the World: The IUCN Red Data Book. Cambridge, England: IUCN.
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Reproduction

Indo-Pacific bottlenosed dolphins are one of the few mammal species in which males cooperate with other males to allow for easier mating with females. Males form alliances with one to three other , potentially unrelated, males. These male groups herd females for mating, sometimes called “mate guarding.” Single males may also attempt to guard females for mating. Breeding females also form groups. Smaller female groups are easier to defend, whereas larger groups of females are difficult to defend. Male and female dolphins tend to mate with more than one partner. Copulation usually occurs when the dolphins are positioned belly to belly in the same direction.

Mating System: polygynandrous (promiscuous) ; cooperative breeder

Female reproductive success depends on the depth of the water; shallow water allows for easier detection of predators and reduced predation overall by sharks. Females reach reproductive maturity between 7 and 12 years of age, this maturation is communicated to males by freckling on the ventral region. Males reach reproductive maturity between 9 and 13 years. The gestation period is about 12 months.

At birth, Indo-Pacific bottlenosed dolphins are between 0.8 and 1.1 m in length and between 9 and 21 kg. Young are born tail first and are able to swim immediately. The highest rates of births are from October to December. The lactation period lasts for about 18 months in captivity and about 32 months in the wild. The teats are enclosed in slits along the urogenital opening. The mean weaning age is 3.5 years. However, a study in Australia found a weaning age ranging from 2.7 to 8 years. Adult females, in a sample population off the coast of Mikura Island, Japan, give birth once every 3 to 4 years.

Breeding interval: Female Indo-Pacific bottlenosed dolphins breed every 4 to 6 years.

Breeding season: The breeding season typically ranges from September to January. However, breeding may occur throughout the year.

Average number of offspring: 1.

Average gestation period: 12 months.

Average weaning age: 42 months.

Average time to independence: 4 years.

Range age at sexual or reproductive maturity (female): 7 to 12 years.

Range age at sexual or reproductive maturity (male): 9 to 13 years.

Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous

Adult female Indo-Pacific bottlenosed dolphins invest a great deal of time and attention in their calves. Even after weaning, calves stay with their mothers for another one to three years.

Adult male Indo-Pacific bottlenosed dolphins provide little or no parental care, instead maximizing their mating opportunities. Males sometimes cooperate to defend groups of females.

Parental Investment: precocial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female); post-independence association with parents

  • Kogi, K., T. Hishii, A. Imamura, T. Iwatani, K. Dudzinski. 2004. Demographic parameters of indo-pacific bottlenose dolphins (Tursiops aduncus) around Mikura Island, Japan. Marine Mammal Science, 20/3: 510-526.
  • Krzyszczyk, E., J. Mann. 2012. Why become speckled? Ontogeny and function of speckling in Shark Bay bottlenose dolphins (Tursiops spp.). Marine Mammal Science, 28/2: 295-307.
  • Mann, J., R. Connor, L. Barre, M. Heithaus. 2000. Female reproductive success in bottlenose dolphins (Tursiops sp.): life history, habitat, provisioning, and group-size effects. Behavioral Ecology, 11/2: 210-219.
  • Möller, L., L. Beheregaray, R. Harcourt, M. Krützen. 2001. Alliance membership and kinship in wild male bottlenose dolphins (Tursiops aduncus) of southeastern Australia. Proceedings of the Royal Society of Biological Sciences, 268: 1941-1947.
  • Nowak, R. 2003. Walker's Marine Mammals of the World. Baltimore, MD: John Hopkins University Press.
  • Reynolds, J., R. Wells, S. Eide. 2000. The Bottlenose Dolphin: Biology and Conservation. Florida: University Press of Florida.
  • Shirihai, H., B. Jarrett. 2006. Whales, Dolphins, and Other Marine Mammals of the World. Princeton, NJ: Princeton University Press.
  • Vaughan, T., J. Ryan, N. Czaplewski. 2011. Mammalogy. Boston, MA: Jones & Bartlett Learning.
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Molecular Biology and Genetics

Molecular Biology

Barcode data: Tursiops aduncus

The following is a representative barcode sequence, the centroid of all available sequences for this species.


There are 2 barcode sequences available from BOLD and GenBank.

Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.

See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

AACCGATGACTATTCTCTACCAATCACAAAGACATTGGTACCCTATATTTACTATTTGGCGCTTGGGCAGGGATAGTAGGTACCGGCCTA---AGTTTGTTGATTCGTGCTGAATTAGGTCAACCTGGCACACTTATCGGAGAC---GACCAGCTTTATAATGTTCTAGTGACAGCTCATGCCTTCGTAATAATTTTCTTTATAGTTATACCTATCATAATTGGAGGTTTTGGGAACTGATTAGTCCCTTTAATA---ATCGGAGCTCCTGACATAGCATTCCCTCGTCTAAACAACATAAGCTTCTGACTACTCCCCCCTTCCTTTCTACTACTAATAGCATCTTCAATAATTGAAGCCGGCGCAGGTACAGGCTGAACTGTTTACCCTCCTCTAGCCGGAAATCTGGCACATGCAGGAGCCTCGGTAGACCTT---ACTATTTTCTCTCTACATTTAGCCGGTGTATCTTCAATCCTTGGAGCTATTAACTTCATCACAACTATCATTAATATAAAGCCACCCGCTATAACTCAATACCAAACACCCCTCTTCGTCTGATCAGTCTTAGTCACAGCAGTCTTACTTTTACTATCATTACCTGTTCTAGCAGCC---GGAATTACTATACTACTAACCGATCGAAATCTAAACACAACCTTTTTCGACCCAGCAGGAGGAGGTGACCCAATCTTATATCAACACTTATTCTGATTTTTTGGCCATCCTGAAGTATATATTTTAATTCTACCCGGCTTTGGAATAATTTCACACATCGTTACTTATTATTCAGGGAAAAAA---GAACCTTTTGGGTATATGGGAATAGTATGAGCTATAGTTTCTATTGGTTTCCTAGGCTTCATTGTATGAGCTCACCATATGTTCACAGTTGGAATAGACGTGGACACACGAGCATATTTTACATCAGCTACTATAATTATCGCAATTCCTACAGGAGTAAAAGTTTTCAGTTGACTA---GCAACACTTCACGGAGGA---AATATTAAATGATCTCCTGCCCTAATATGAGCTCTAGGCTTTATCTTCTTATTCACAGTAGGAGGTCTAACCGGTATTATCCTAGCTAACTCATCCCTAGATATCATCCTTCATGACACCTATTATGTAGTTGCTCATTTTCACTATGTG---CTTTCAATAGGAGCTGTCTTTGCCATCATAGGAGGCTTCGTTCACTGATTCCCACTATTTTCAGGGTATACACTCAACCCAACATGAACAAAAATTCAATTCGTAATTATATTCGTAGGTGTAAATATGACATTCTTCCCACAACACTTCCTAGGCCTATCTGGAATGCCTCGC---CGATATTCTGACTATCCAGATGCTTACACA---ACATGAAACACCATTTCATCAATAGGCTCATTTATCTCACTAACAGCAGTTATACTAATAATCTTTATTATCTGAGAAGCATTCGCATCTAAACGAGAGGTA---TTAGCGGTAGACCTCACTTCCACAAAC
-- end --

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Statistics of barcoding coverage: Tursiops aduncus

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 2
Specimens with Barcodes: 2
Species With Barcodes: 1
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Conservation

Conservation Status

Hunting and shark nets have historically threatened populations of bottlenosed dolphins because these dolphins, especially Indo-Pacific bottlenosed dolphins, prefer shallow coastal waters. These dolphins are killed for meat, fertilizer, cooking oil, and machine lubrication.

US Federal List: no special status

CITES: appendix ii

State of Michigan List: no special status

  • Hammond, P., G. Bearzi, A. Bjørge, K. Forney, L. Karczmarski, T. Kasuya, W. Perrin, M. Scott, J. Wang, R. Wells, B. Wilson. 2008. "Tursiops aduncus" (On-line). IUCN Red List of Threatened Species. Accessed February 10, 2012 at www.iucnredlist.org.
  • Lipscomb, T., F. Schulman, D. Moffett, S. Kennedy. 1994. Morbilliviral Disease in Atlantic Bottlenose Dolphins (Tursiops truncatus) from the 1987-1988 Epizootic. Journal of Wildlife Diseases., 30/4: 567-571.
  • Van Bressem, M., K. Waerebeek, P. Jepson, J. Raga, P. Duignan, O. Nielsen, A. DiBeneditto, S. Siciliano, R. Ramos, W. Kant, V. Peddemors, R. Kinoshita, P. Ross, A. López-Fernandez, K. Evans, E. Crespo, T. Barrett. 2001. An insight into the epidemiology of dolphin morbillivirus worldwide. Veterinary Microbiology, 81/4: 287-304.
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IUCN Red List Assessment


Red List Category
DD
Data Deficient

Red List Criteria

Version
3.1

Year Assessed
2012

Assessor/s
Hammond, P.S., Bearzi, G., Bjørge, A., Forney, K.A., Karkzmarski, L., Kasuya, T., Perrin, W.F., Scott, M.D., Wang, J.Y. , Wells, R.S. & Wilson, B.

Reviewer/s
Rojas-Bracho, L. & Smith, B.D.

Contributor/s

Justification
Although the species is widespread in Indo-pacific coastal waters and its aggregate abundance is probably in the tens of thousands in multiple local populations, habitat destruction and incidental takes (of unknown but possibly large magnitude) may have a significant impact on this species. However, the lack of available information precludes an assessment of this impact.

History
  • 1996
    Data Deficient
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Status in Egypt

Unknown, probably accidental.

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Population

Population
Few estimates of abundance have been made. There are estimated to be 520–530 Bottlenose Dolphins off KwaZulu-Natal, South Africa, most of which are probably T. aduncus (the rest T. truncatus – Cockcroft et al. 1992). Between 136 and 179 (95% Cis = 124-212) are known off Zanzibar, Tanzania (Stensland et al. 2006); at least 1,200 in the Persian Gulf (Preen 2004); at least 400 photo-identified along the rim of the Swatch-of-No-Ground, Bangladesh (Rubaiyat Mansur Mowgli and Brian D. Smith pers. comm.); about 218 off western Kyushu, Japan (Shirakihara et al. 2002); 169 off Mikura Island, Japan (Kogi et al. 2004); low tens at the southern tip of Taiwan and about 50 from the northeastern Philippines (J. Y. Wang pers. comm.); 1,099 off Queensland, eastern Australia (Chilvers and Corkeron 2003) and at least 2,000–3,000 in Shark Bay western Australia (Preen et al. 1997).

Population Trend
Unknown
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Threats

Major Threats
The species’ near-shore distribution makes it vulnerable to environmental degradation, direct exploitation, and fishery conflicts (Curry and Smith 1997, Wells and Scott 1999; Reeves et al. 2003). Until hunting was outlawed in 1990, this species was hunted in a large-scale drive fishery in Taiwan’s Penghu Islands. Some Indo-Pacific Bottlenose Dolphins are taken in the small cetacean fisheries of Sri Lanka.

Incidental catches occur in a number of fisheries throughout the range, including gillnets and purse seines. A Taiwanese shark gillnet fishery operated in northern Australian waters during the early 1980s and took up to 2,000 per year (Harwood and Hembree 1987). Incidental catch in Taiwan continues to be a serious problem. For example, multiple individuals have been seen observed in single catches there and throughout most of the species’ range (J.Y. Wang pers. comm.). A large proportion of dolphins (~40%) off Bangladesh exhibit scars and mutilations consistent with rope and net entanglement in trawl and gill-net fisheries (Rubaiyat Mansur Mowgli and Brian D. Smith pers. comm.). In South Africa and Australia, Indo-Pacific Bottlenose Dolphins also suffer considerable mortality in the large-mesh nets set to protect bathers from sharks (Peddemors 1999, Reeves et al. 2003).

Live-captures for oceanarium display have taken place in Taiwan, Indonesia and the Solomon Islands in recent years from unassessed populations; their preference as a captive display species makes them vulnerable to depletion from such catches (Wang et al. 1999, Reeves et al. 2003, Kahn ).

Indo-Pacific Bottlenose Dolphins in coastal areas are exposed to a wide variety of threats in addition to direct and indirect takes. Threats that are cause for concern include: 1) the toxic effects of xenobiotic chemicals; 2) reduced prey availability caused by environmental degradation and overfishing (Jackson et al. 2001); 3) direct and indirect disturbance and harassment (e.g. boat traffic and commercial dolphin watching and interactive programs); 4) marine construction and demolition and 5) other forms of habitat destruction and degradation (including anthropogenic noise). Although these and other threats are technically challenging to quantify by comparison with takes, their cumulative impact is likely to result in longitudinal population declines. Lack of historical data in many cases hampers understanding of long-term trends, possibly resulting in shifting baselines.
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Management

Conservation Actions

Conservation Actions
The species is listed in Appendix II of CITES.

More research is needed to establish the range and clarify the taxonomy of the genus Tursiops. More information is also needed on population size and the extent and magnitude of direct and indirect takes so that their impact on this species can be assessed.
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Relevance to Humans and Ecosystems

Benefits

There are no known adverse effects of Tursiops aduncus on humans.

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At some sites, Indo-Pacific bottlenosed dolphins have been habituated to the presence of human swimmers. At Mikura Island, Japan, there is a dolphin swim program in the summer that began in the 1990’s. Bottlenosed dolphins are common in marine exhibits and zoos. They can be easily trained to perform agile displays and to play with and locate objects. However, Indo-Pacific bottlenosed dolphins are generally more shy and less inquisitive than other bottlenosed dolphins. Like other marine mammals, the lifespan of these dolphins in captivity is significantly shorter than in the wild and there are significant ethical concerns with keeping such large, intelligent mammals in captive conditions.

Positive Impacts: food ; ecotourism ; research and education

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Risks

IUCN Red List Category

Data Deficient (DD)
  • IUCN (2008) Cetacean update of the 2008 IUCN Red List of Threatened Species.
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Indo-Pacific bottlenose dolphin

Indo-Pacific bottlenose dolphin!<-- This template has to be "warmed up" before it can be used, for some reason -->

The Indo-Pacific bottlenose dolphin (Tursiops aduncus) is a species of bottlenose dolphin. The Indo-Pacific bottlenose dolphin grows to 2.6 metres (8.5 ft) long, and weigh up to 230 kilograms (510 lb).[3] It lives in the waters around India, northern Australia, South China, the Red Sea, and the eastern coast of Africa.[3] Its back is dark-grey and belly is lighter grey or nearly white with grey spots. [3]

Until 1998, all bottlenose dolphins were considered members of the single species T. truncatus. In that year, the Indo-Pacific bottlenose dolphin was recognized as a separate species.[4][5] The Indo-Pacific bottlenose dolphin is generally smaller than the common bottlenose dolphin, has a proportionately longer rostrum, and has spots on its belly and lower sides.[4][6] The Indo-Pacific bottlenose dolphin also has more teeth than the common bottlenose dolphin — 23 to 29 teeth on each side of each jaw for the Indo-Pacific bottlenose dolphin, compared to 21 to 24 for the common bottlenose dolphin.[6] There is evidence that the Indo-Pacific bottlenose dolphin may actually be more closely related to certain dolphin species in the genera Stenella and Delphinus, especially the Atlantic Spotted Dolphin (S. frontalis), than it is to the common bottlenose dolphin.[4][7]

Much of the old scientific data in the field combine data about the Indo-Pacific bottlenose dolphin and the common bottlenose dolphin into a single group, making it effectively useless in determining the structural differences between the two species. The IUCN lists both species as data deficient in their Red List of endangered species because of this issue.[8]

Contents

Description

Indo-Pacific bottlenose dolphins are very similar to common bottlenose dolphins in appearance. Common bottlenose dolphins have a reasonably strong body, moderate-length beak, and tall curved dorsal fins whereas Indo-Pacific bottlenose dolphins are have a more slender body build and their beak is longer and more slender.[9] The Indo-Pacific population also tends to have a somewhat lighter blue colour and the cape is generally more distinct with a light spinal blaze extending to below the dorsal fin.2 However, although not always present, the most obvious distinction came be made with the presence of black spots or flecks on the bellies of adults of Indo-Pacific bottlenose dolphins which are very rare in common bottlenose dolphins.[9] Their teeth can number between 23 and 29 in each upper and lower jaw and are more slender than those of common bottlenose dolphins.[9] Size of Indo-Pacific bottlenose dolphins can vary based on geographic location however its average length is 2.6 metres (8.5 ft) long, and it weighs up to 230 kilograms (510 lb).[3] Their length at birth is between 0.84 and 1.5 metres (2.8 and 4.9 ft).[3]

Diet

Indo-Pacific bottlenose dolphins feed on a wide variety of fish and cephalopods (particularly squid).[10]

In a recent study conducted by Amir et al. (2005)[10] researchers looked at the feeding ecology of Indo-Pacific bottlenose dolphins by analyzing the stomach contents of ones that got caught in the gillnet fisheries off Zanibar, Tanzania. The prey items found in the stomach contents included 50 species of bony fish and 3 species of squid. From their results the researchers concluded that the most important prey group was fish which accounted for 87% of the total number of prey items consumed and occurred in 24 of 26 stomachs examined. Cephalopods comprised the other 13% of prey items and were found in 13 of the 26 stomachs.[10] The remains of some crustaceans were also found however they hypothesize that they were consumed secondarily since a number were found intact in the fish prey stomachs and therefore were not included in the diet analysis.[10]

Behavior

Indo-Pacific bottlenose dolphins live in groups that can number in the hundreds, but groups of 5 to 15 dolphins are most common.[6] In some parts of their range they associate with the common bottlenose dolphin.[6] It also associates with other dolphin species, such as the humpback dolphin.[6]

The Indo-Pacific bottlenose dolphin has a peak mating and calving season in spring and summer, although mating and calving occur throughout the year in some regions. Gestation period is about 12 months. Calves are between 0.84 and 1.5 metres (2.8 and 4.9 ft) long, and weigh between 9 and 21 kilograms (20 and 46 lb). The calves are weaned between 1.5 and 2 years, but can remain with their mother for up to 5 years. The interbirth interval for females is typically 4 to 6 years.[3]

In some parts of its range, the Indo-Pacific bottlenose dolphin is subject to predation by sharks.[6] The Indo-Pacific bottlenose dolphin can live more than 40 years.[3]

Indo-Pacific bottlenose dolphins located in Shark Bay, Australia are thought to have a symbiotic relationship with sponges by doing what is called “sponging”. What happens is a dolphin breaks a marine sponge off the sea floor and wears it over its rostrum. It is thought that the reason they do this is to probe substrates for fish however it is still not completely understood if it is used for a tool or simply for play.

Status and threats

Indo-Pacific bottlenose dolphins are not considered to be endangered as a species however, it has a near-shore distribution which makes it vulnerable to environmental degradation, direct exploitation, and problems associated with local fisheries.[11]

The major predators of this species are typically sharks however some others may include humans, killer whales (Orcinus orca) and sting rays. Just recently large numbers of these dolphins were deliberately killed in a Taiwanese drive fishery which greatly impacted the species.[citation needed] It is now prohibited. However, gillnets are still having an impact and are a problem not only here but throughout most of the species’ range. In the early 1980s many were killed in a Taiwanese driftnet fishery in the Arafura Sea, off northwestern Australia.[12] Large-mesh nets set to protect bathers from sharks in South Africa and Australia has also resulted in a substantial number of deaths in the Indo-Pacific bottlenose dolphins.[13]

Captivity

Indo-Pacific dolphins are one of many small cetaceans commonly found in captivity.[10] Some of the conservation concerns for animals in captivity include: the effects of removing the animals from their wild populations, survivorship of cetaceans during capture and transport and while in captivity and the risks to wild populations and ecosystems of accidentally introducing alien species and spreading epizootic diseases, especially when animals have been transported over long distances and are held in sea pens.[14]

Bottlenose dolphins are the most common captive cetaceans on a global scale.[14] Prior to 1980 more than 1,500 bottlenose dolphins were collected from the United States, Mexico, and the Bahamas and more than 550 common and 60 Indo-Pacific bottlenose dolphins were brought into captivity in Japan.[14] By the late 1980s, the United States stopped collecting bottlenose dolphins and the number of captive-born animals in North American aquariums has increased from only 6 percent in 1976 to about 44 percent in 1996.

Effects of whale watching

Not much is known about the impact of whale watching on cetaceans but research is being conducted at several locations.

Japan

Morisaka et al. (2005)[15] conducted a study on three populations of Indo-Pacific bottlenose dolphins in Japan. It is believed that characteristics of acoustic signals are affected by the acoustic environments among habitats and geographical variation in animal acoustic signals can result from differences in acoustic environments therefore the characteristics of the ambient noise in the dolphin's habitats and the whistles produced were compared. Ambient noise was recorded using a hydrophone located 10m below the surface and whistles were recorded by using an underwater video system.

Results showed that dolphins produced whistles at varying frequencies with greater modulations when in habitats with less ambient noise whereas habitats with greater ambient noise seem to cause dolphins to produce whistles of lower frequencies and fewer frequency modulations. Examination of the results suggest that communication signals are adaptive and are selected to avoid the masking of signals and the decrease of higher-frequency signals as Tadamichi et al. states in the paper. They concluded that ambient noise has the potential to drive the variation in whistles of Indo-Pacific bottlenose dolphin populations.

Jervis Bay, Australia

Small motorized vessels have increased as a source of anthropogenic noise due to the rise in popularity of wildlife viewing such as whale-watching. Lemon et al. (2006)[16] carried out a study in Australia on bottlenose dolphins to look at whether powerboats are in fact a significant source of disturbance for these animals. The surface behaviour and acoustic response of traveling dolphins to approaches by a powerboat were assessed by a series of experimental trials. Dolphin behaviour was monitored continuously from an independent research boat before, during, and after a powerboat approached. Once a group of traveling dolphins was located, the group was randomly assigned to either a control or treatment condition. During each experimental trial the dolphin's acoustic and surface behaviour were recorded "pre-exposure" with the powerboat stationary and engine off, "on-approach" with the powerboat approaching the focal group, "exposure" with the power boat moving slowly alongside the group, and "post-exposure" when the powerboat had departed from the area. For the control trials the surface and acoustic behaviours were recorded from the research vessel where only the electric motor was used.

Results of the study showed that powerboat approaches altered the surface behaviour and direction of traveling dolphins when exposed to vessels within 100m. Their whistles and echolocation click bouts however, were not affected when approached. When powerboats approached the dolphins they changed their surface behaviour from traveling to milling and changed their direction to travel away from the powerboat. It was not until the powerboat left the area and its noise ceased that the dolphins returned to their preceding behaviour in the original direction.

Shark Bay, Australia

Another study was carried out by Bejder et al. (2006)[17] in Shark Bay, Western Australia on the behavioural responses of Indo-Pacific bottlenose dolphins to experimental vessel approaches in regions of both high and low vessel traffic. Data was collected from two different sites that had different histories of vessel activity: high vessel activity classified as the impact site and low vessel activity classified as the control site. A team of researchers evaluated group-level, non-vocal, behavioural responses of dolphins 15 minutes before, during and after approaches by an experimental vessel. For each experiment observers selected a focal dolphin group based on the group's proximity to the shore station and the absence of any vessels within 300m. After the focal group was selected, observers on the shore recorded behavioural data for 15 minutes. Then vessel-based observers were directed towards the focal group and collected data once within 50m of the group. Throughout the 15 minute period, shore observers continued to record behavioural data while the vessel maintained a distance of 10-50m from the focal group. Observers aboard the experimental vessel identified individual dolphins in the focal group taking dorsal fin photographs. When the experimental vessel was beyond 300m of the focal group, the shore team continued to monitor the behaviour and movements of the focal group for another 15min. Tour vessel movements were also tracked using GPS to show focal group movements during the experiment.

Results show that there were significant changes in the behaviour of targeted dolphins when compared with their behaviour before and after approaches. Dolphins in the control site showed a stronger and longer-lasting response than dolphins in the impact site. It is believed that these results show habituation of the dolphins to the vessels in a region of long-term vessel traffic. However, when compared to other studies in the same area, it is suggested that this study documented moderated responses not because of habituation occurring but because those individuals sensitive to vessel disturbance left the region before their study began.

Although these studies do show statistical significance for the effects of whale-watching boats,these results do not have biological significance and need to be researched further.

References

  1. ^ Mead, James G.; Brownell, Robert L., Jr. (16 November 2005). "Order Cetacea (pp. 723-743)". In Wilson, Don E., and Reeder, DeeAnn M., eds. Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Baltimore: Johns Hopkins University Press, 2 vols. (2142 pp.). ISBN 978-0-8018-8221-0. OCLC 62265494. http://www.bucknell.edu/msw3/browse.asp?id=14300098. 
  2. ^ Hammond, P.S., Bearzi, G., Bjørge, A., Forney, K., Karczmarski, L., Kasuya, T., Perrin, W.F., Scott, M.D., Wang, J.Y., Wells, R.S. & Wilson, B. (2008). Tursiops aduncus. In: IUCN 2008. IUCN Red List of Threatened Species. Downloaded on 7 October 2008.
  3. ^ a b c d e f g Shirihai, H. and Jarrett, B. (2006). Whales Dolphins and Other Marine Mammals of the World. p. 159–161. ISBN 0-691-12757-3. 
  4. ^ a b c Wells, R. and Scott, M. (2002). "Bottlenose Dolphins". In Perrin, W.; Wursig, B. and Thewissen, J.. Encyclopedia of Marine Mammals. Academic Press. p. 122–127. ISBN 0-12-551340-2. 
  5. ^ Möller Luciana M., Beheregaray Luciano B. 2001. Coastal bottlenose dolphins from southeastern Australia are Tursiops aduncus according to sequences of the mitochondrial DNA control region. Marine Mammal Science 17(2): 249-263.
  6. ^ a b c d e f Reeves, R.; Stewart, B.; Clapham, P.; Powell, J. (2002). Guide to Marine Mammals of the World. p. 362–365. ISBN 0-375-41141-0. 
  7. ^ Leduc, R., Perrin, W. & Dizon, E. (August 18, 1998). "Phylogenetic Relationships among the Delphinid Cetaceans Based on Full Cytochrome B Sequences". Marine Mammal Science 15 (3): 619–648. doi:10.1111/j.1748-7692.1999.tb00833.x. http://www3.interscience.wiley.com/journal/119937779/abstract. Retrieved 2008-10-05. 
  8. ^ "Tursiops truncatus: Species Information". IUCN. http://www.iucnredlist.org/search/details.php?species=22563. Retrieved 2006-11-03. 
  9. ^ a b c Worlds Creatures. 2004. Indo-Pacific bottlenose dolphin. Retrieved March 28, 2008 from the website: http://www.worldscreatures.com/water-species/dolphins/indo-pacific-bottlenose-dolphin.htm.
  10. ^ a b c d e Amir Omar A., Per Berggren, Simon Ndaro G.M., Narriman Jiddawi S. 2005. Feeding ecology of the Indo-Pacific bottlenose dolphin (Tursiops aduncus) incidentally caught in the gillnets fisheries off Zanzibar, Tanzania. Estuarine, Coastal and Shelf Science 63(3): 429-437.
  11. ^ Curry, B.E. and Smith, J. 1997. Phylogeographic structure of the bottlenose dolphin (Tursiops truncatus): stock identification and implications for management. In: A.E. Dizon, S.J. Chivers, and W.F. Perrin (eds) Molecular Genetics of Marine Mammals, pp. 227-247. Society for Marine Mammalogy, Special Publication No. 3, Allen Press, Lawrence, Kansas.
  12. ^ Harwood, M.B. and Hembree, D. 1987. Incidental catch of small cetaceans in the offshore gillnet fishery in northern Australian waters: 1981-1985. Report of the International Whaling Commission 37: 363-367.
  13. ^ Peddemors, V.M. 1999. Delphinids of southern Africa: a review of their distribution, status and life history. Journal of Cetacean Research and Management 1: 157-165.
  14. ^ a b c Fisher Sue J., Reeves Randall R. 2005. The Global Trade in Live Cetaceans: Implications for Conservation. Journal of International Wildlife Law and Policy 8: 315-340
  15. ^ Morisaka Tadamichi, Shinohara Masanori, Nakahara Fumio, Akamatsu Tomonari. 2005. Effects of Ambient Noise on the Whistles of Indo-Pacific Bottlenose Dolphin Populations. Journal of Mammalogy 84(3): 541-546.
  16. ^ Lemon Michelle, Lynch Tim P., Cato Douglas H., Harcourt Robert G. 2006. Response of traveling bottlenose dolphins (Tursiops aduncus) to experimental approaches by a powerboat in Jervis Bay, New South Wales, Australia. Biological Conservation 127:363-372
  17. ^ Bejder Lars, Samuels Amy, Whitehead Hal, Gales Nick. 2006. Interpreting short-term behavioural responses to disturbance within a longitudinal perspective. Animal Behaviour 72: 1149-1158

Further reading

Cockcroft VG, Ross GJB. 1990. Age, growth, and reproduction of bottlenose dolphins Tursiops truncatus from the east coast of southern Africa. Fishery Bulletin 88(2): 289-302.

Moller Luciana M., Beheregaray Luciano B., Allen Simon J., Harcourt Robert G. 2006. Association patterns and kinship in female Indo-Pacific bottlenose dolphins (Tursiops aduncus) of southeastern Australia. Behavioural Ecology Sociobiology 61: 109-117.

Nowacek Stephanie M., Wells Randall S., Solow Andrew R. 2001. Short-term effects of boat traffic on bottlenose dolphins, Tursiops truncatus, in Sarasota Bay, Florida. Marine Mammal Science 17(4): 673-688.

Schroeder, J. Pete. Breeding Bottlenose Dolphins in Captivity. In The Bottlenose Dolphin, edited by Stephen Leatherwood and Randall R. Reeves, pp. 435-446. San Diego: Academic Press, Inc., 1990.

Shane Susan H., Wells Randall S., Wursig Bernd. 1986. Ecology, behaviour and social organization of the bottlenose dolphin: a review. Marine Mammal Science 2(1): 34-63.

Urian, K.W., Duffield D.A., Read A.J., Wells R.S., Shell E.D. 1996. Seasonality of Reproduction in Bottlenose Dolphins, Tursiops truncatus. Journal of Mammalogy, 77(2): 394-403.

Wells, Randall S., Scott Michael D., Irvine Blair A. The Social Structure of Free-ranging Bottlenose Dolphins. In Current Mammalogy, Volume 1, edited by H.H. Genoways, pp. 247- 305. New York: Plenum Press, 1987.

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